We're not that serious. We just want him to play fun music.
Every piano teacher has heard this at least a few dozen times. It's usually the first sign of the end, unfortunately.
Not because learning music isn't fun. Not because the act of playing music isn't fun. And not because listening to music isn't fun.
But, music as an entity is incapable of being fun. Just the same way music can't do chores, babysit the kids, or pay the bills.
We humans bring the fun to music. And we humans experience fun as we listen to it. A whole range of other emotions, too.
Sometimes, there is a perception that the "fun music" is music that requires little effort or discipline from the learner. Fun like one would experience at a water park, movie theater, or arcade (if you can find a good one anymore...).
This definition of fun music is like the unicorn. A nice thought, but mostly make believe. All music requires some work.
And that is where the fun lies.
The fun of piano is in the adventure. Enjoying the process of building skills and learning the language of music. Relishing in every moment you learn something new. Declaring unquestioned victory over every challenge. And getting to share it all with other people.
So, stop trying to find fun music. Go have fun making music instead.